JPH114040A - Surface light-emitting laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface light-emitting semiconductor laser, capable of reducing a threshold value further, lowering power consumption and improving efficiency, and the manufacturing method of the surface light-emitting semiconductor laser with superior controllability for facilitating the manufacture. SOLUTION: In this surface light-emitting laser provided with an active layer 1 and a pair of distributed reflection layers (DBRs) 3 and 6 for holding the active layer 1 there between and forming a resonator on a substrate 7, an oxidized layer 5 for current constriction provided with an opening part is provided on a position near the active layer 1 between the active layer 1 and the distributed reflection layer 3 and the oxidized layer 4 for light constriction of a large film thickness and an opening wider than the oxidized layer 5 for the current constriction is provided on the position separated more than the oxidized layer 5 for the current constriction from the active layer 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface emitting laser, and more particularly, to a surface emitting laser capable of reducing a threshold current and reducing power consumption of the surface emitting laser and a method of manufacturing the same.

[0002]

2. Description of the Related Art A surface emitting laser is a laser that emits light in a direction perpendicular to a substrate, and is used as a light source for optical interconnection and the like. For example, JP-A-3-3
Japanese Patent No. 4754 describes a structure using a resonator formed of a semiconductor multilayer reflective film having a GaAs / AlAs laminated structure and a current confinement structure in which a high-resistance layer is formed beside an active layer by ion implantation.

On the other hand, Electronics Letters,
Vol. 30, p. 2043 states that a laser having excellent characteristics of low threshold and high efficiency can be obtained by forming a current confinement structure by oxidizing a part of the AlAs or AlGaAs film in the constituent material. Is described. In this manufacturing method, oxidation of AlGaAs by steam at a high temperature is used. By making use of the fact that the oxidation rate increases as the Al composition ratio increases from 0 to 1, by increasing the Al composition ratio of one layer immediately adjacent to the active layer, only this one layer is oxidized from the surroundings. Is the way.

An Al (Ga) As oxide layer formed by oxidizing the periphery of an Al (Ga) As layer having a large Al composition ratio has a high resistance and thus functions as a current confinement layer. At the same time, Al
The (Ga) As oxide layer has a refractive index of the original Al (G
a) Since it is lower than that of the As layer, it also functions as a light confinement layer caused by a difference in refractive index. Therefore, a surface emitting laser using this selective oxidation has a very small threshold value of several tens of μA because current is injected only into a very small region and light is confined.

[0005]

However, when the current confinement by oxidation is further advanced to further reduce the threshold current,
If the opening diameter is 3 μm or less, there is a problem that the threshold current increases. Applied Physics Letters
Vol. 70, pages 823-825 (AppliedPhy
sics Letters, 70 (7), pp823-
According to 825, 1997), it is considered that when the diameter is small, light is diffracted due to a difference in refractive index between the oxide layers.

It is an object of the present invention to provide a surface-emitting type semiconductor laser in which the threshold value is further reduced to achieve low power consumption and high efficiency, and a method of manufacturing a surface-emitting type semiconductor laser which is easy to manufacture and has excellent controllability. Aim.

[0007]

SUMMARY OF THE INVENTION The present invention relates to a surface emitting laser having an active layer on a substrate and a set of distributed reflection layers forming a resonator with the active layer interposed therebetween. A current confinement oxide layer having an opening is provided at a position near the active layer between the layers, and at a position farther from the active layer than the current confinement oxide layer, an opening wider than the current confinement oxide layer is provided.
The present invention relates to a surface-emitting laser provided with a thick optical confinement oxide layer.

The present invention also relates to a method of manufacturing a surface emitting laser having an active layer on a substrate and a set of distributed reflection layers forming a resonator with the active layer interposed therebetween. Forming a layer, forming an active layer, forming a first high Al semiconductor compound layer having a higher Al composition ratio than other layers, and forming an Al layer from the first high Al semiconductor compound layer. A step of forming a second high Al semiconductor compound layer having a low composition ratio and a higher Al ratio than the other layers, a step of forming another distributed reflection layer, and at least a first and a second high Al semiconductor The present invention relates to a method for manufacturing a surface emitting laser, which includes a step of processing a compound layer into a mesa shape and a step of oxidizing first and second high Al semiconductor compound layers from the surroundings in an atmosphere containing water vapor.

In the present invention, the current confinement can be sufficiently performed by providing the current confinement oxide layer having a small opening at a position between the active layer and the distributed reflection layer close to the active layer. Further, by making the layer thickness thin enough that light does not perceive a change in the refractive index, light scattering and diffraction loss due to the change in the refractive index can be minimized.

Further, a light confinement oxide layer having a large thickness and a wide opening is provided at a position slightly further from the current confinement oxide layer as viewed from the position of the active layer, thereby sufficiently confining light. be able to. That is, according to the present invention, by separately providing an oxide film having a current confinement function and an oxide film having a light confinement function, optimal conditions can be set for each of them, thereby realizing laser oscillation with a lower threshold current than before. can do.

Further, in the manufacturing method of the present invention, by increasing the Al composition ratio of the two layers in the compound semiconductor laminated structure, only the two layers are oxidized, and even between these two layers, By changing the Al composition ratio, the rate of steam oxidation from the surroundings is adjusted. As a result, oxide films having different openings can be formed accurately.

[0012]

Next, an embodiment of the present invention will be described in detail with reference to FIG.

On a semiconductor substrate 7, an active layer 1 and a distributed reflection layer DBR6 (Distribute) on the substrate side sandwiching the active layer 1 are provided.
d Bragg Reflector) and a resonator including the upper DBR 3. Above and below the active layer 1, an intermediate layer 2 is provided to constitute a resonator.
A thin oxide layer 5 for current confinement, which is thin enough that light does not sense a difference in refractive index, is provided immediately above the layer. The current confinement oxide layer 5 is an oxide film having a non-oxidized semiconductor opening B9 at the center.

For example, when the oscillation wavelength is 980 nm, if the refractive index of the semiconductor is about 3, the wavelength of the light in the semiconductor becomes about 300 nm.
(Wavelength) / 4, that is, a thickness of about 80 nm. The thickness of the current confinement oxide layer is approximately 1/4 of this thickness,
That is, about 20 nm is appropriate. However, when the position of the current confinement oxide layer 5 is away from the active layer, the thickness is usually large.
It is preferable to reduce the thickness when approaching, and to decrease as the change in the refractive index of the oxide layer increases. In addition, the thickness and the distance from the active layer are appropriately adjusted and optimized in accordance with the purpose of each laser and the like, since it depends on the light emission intensity and the diameter of the opening B9. Here, the thickness of the current confinement oxide layer is set to 15 nm.
And

The smaller the diameter of the opening B9 is, the more the current constriction is performed. Therefore, the threshold current is lowered. However, the light emission efficiency is lowered due to heat generation due to an increase in resistance and the gain is saturated. Also need to be optimized for individual lasers. Here, the diameter was 2.5 μm.

An oxide layer 4 for light confinement is provided at a position (wavelength) / 2 away from the intermediate layer 2. This thickness is such that light can sufficiently change the refractive index, and is thicker than the current confinement oxide layer 5. As a guide, (wavelength) / 4, that is, about 80 nm may be used. However, in order to avoid loss due to light diffraction and scattering, when the distance from the active layer 1 is small, the thickness needs to be reduced.

The diameter of the opening A8 needs to be optimized for each laser so that diffraction and scattering losses are small while maintaining the light confinement effect. In the present invention, the diameter is set to 5 μm.

By narrowing the current to the opening B9 which is sufficiently narrow without causing light scattering and scattering loss by the thin current confinement oxide layer 5, and achieving light confinement by the thick light confinement oxide layer 4, The threshold value can be reduced to the extent that one oxide layer could not.

Next, a method of manufacturing the laser structure will be described below. As a film formation method, a molecular beam epitaxy method or a metal organic vapor phase epitaxy method can be used.

As shown in FIG. 2, on a GaAs substrate 7,
The set of Al _x Ga _{1 -x} As / GaAs (x = 0.92) is 2
2.5 sets (the lowermost layer and the uppermost layer were Al _x Ga _{1 -x} As layers) were formed to form a substrate-side DBR 6 having a thickness of about 2.9 μm.

On top of this, an intermediate layer is formed of Al _x Ga _{1 -x} As (x =
0.2), and an active layer was formed thereon with In _x Ga
_1-x As (x = 0.2) composition, 3 quantum well layers, thickness 1
0 nm, and an intermediate layer is further formed thereon by Al _x Ga _1-x
A film was formed with a composition of As (x = 0.2). The thickness of the intermediate layer is one wavelength, about 0.3 μm in optical length, including both the upper and lower portions of the active layer.

On top of this, an Al _x Ga _{1 -x} As (x = 0.97) layer 15 for forming a current confinement oxide layer in a later step
Was formed into a film having a thickness of 15 nm.

Next, a GaAs layer is formed thereon with a 波長 wavelength,
The film was formed to a thickness of about 50 nm.

An Al _x Ga _{1 -x} As (x = 0.95) layer 14 for forming an optical confinement oxide layer in a later step was formed thereon to a thickness of 60 nm.

Further, on top of this, Al _x Ga _{1 -x} As / Ga
A set of As (x = 0.92) was formed into a 15.5 composition film to form an upper DBR 3 having a thickness of about 2.0 μm.

By the steps described above, a laminated structure as shown in FIG. 2 is obtained. From the upper DBR to a part of the substrate-side DBR of this laminated structure, a mesa having a diameter of 40 μm is processed as shown in FIG. 430 ° C in a nitrogen atmosphere containing water vapor
For 10 minutes.

As a result, Al _x Ga _{1 -x} having a large Al composition ratio
Oxidation of the As (x = 0.97) layer 15 progresses to the middle to form a current confinement oxide layer 5 having a small opening, and Al _x Ga _{1 -x} As having a smaller Al composition ratio than this. (X =
0.95) In layer 14, oxidation progressed to the middle,
Light confinement oxide layer 4 having an opening larger than current confinement oxide layer 4
Was formed, and the surface emitting laser shown in FIG. 1 was obtained.

As described above, in the manufacturing method of the present invention, the rate of steam oxidation can be adjusted by changing the Al composition ratio, so that oxide films having different openings can be formed with high accuracy. Conditions such as the temperature and time of steam oxidation can be appropriately adjusted according to the process.

[0029]

According to the present invention, it is possible to further reduce the threshold value as compared with the conventional structure, thereby achieving low power consumption and high efficiency. Further, according to the manufacturing method of the present invention, it is possible to provide a method of manufacturing a surface emitting semiconductor laser which is easy to manufacture and has excellent controllability.

[Brief description of the drawings]

FIG. 1 is a diagram showing a surface emitting laser of the present invention.

FIG. 2 is a diagram showing a manufacturing process of the surface emitting laser of the present invention.

FIG. 3 is a view showing a manufacturing step of the surface emitting laser of the present invention, following FIG. 2;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Active layer 2 Intermediate layer 3 Upper DBR 4 Light confinement oxide layer 5 Current confinement oxide layer 6 Substrate side DBR 7 Substrate 8 Opening A 9 Opening B 14 Al _x G to be a light confinement oxide layer in a later step
a _1-x As (x = 0.95) layer 15 Al _x to be a current confinement oxide layer in a later step
Ga _1-x As (x = 0.97) layer

Claims (2)

[Claims] 1. A surface emitting laser having an active layer on a substrate and a set of distributed reflection layers forming a resonator with the active layer interposed therebetween, wherein the surface emitting laser is close to the active layer between the active layer and the distributed reflection layer. A current confinement oxide layer having an opening is provided at a position, and a light confinement oxide layer having a larger opening and a larger film thickness than the current confinement oxide layer is provided at a position farther from the active layer than the current confinement oxide layer. A surface emitting laser provided. 2. A method of manufacturing a surface emitting laser having an active layer on a substrate and a pair of distributed reflection layers forming a resonator with the active layer interposed therebetween, comprising forming one distributed reflection layer on the substrate. Forming a film, forming an active layer, forming a first high Al semiconductor compound layer having a higher Al composition ratio than the other layers, and forming a first high Al semiconductor compound layer having a higher Al composition ratio than the other layers. Forming a second high Al semiconductor compound layer having a lower Al ratio than the other layers; forming another distributed reflection layer; and forming at least the first and second high Al semiconductor compound layers. A method for manufacturing a surface emitting laser, comprising: a step of processing into a mesa type; and a step of oxidizing a first and a second high Al semiconductor compound layer from the surroundings in an atmosphere containing water vapor.